JPH107641A - Production of esocyanate compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject compound useful as a raw material for producing industrial products in a wide field such as polyurethane foam, elastomer and coating material in high yield stably for a long period of time. SOLUTION: A formamide compound in an amount of 1mol is reacted with dimethyl carbonate in a molar ratio of 0.1-20 in the presence of methanol, taking out formed methyl formate from the system by reaction distillation and thermally decomposing a prepared urethane compound in the presence of an inert solvent and a compound of the formula Xn-Ar-SO2 -NH2 (Ar is benzene, naphthalene, etc.; X is an alkyl or amino; (n) is an integer of 0-30) (e.g. p toluenesulfonamide). In the production, preferably a reactor made of a metal material is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for synthesizing a urethane compound using a formamide compound and dimethyl carbonate as starting materials, and then producing the corresponding isocyanate compound by thermal decomposition of the urethane compound.

[0002]

2. Description of the Related Art Isocyanate compounds are extremely reactive substances and are used as raw materials for manufacturing industrial products in a wide range of fields, such as polyurethane foams, elastomers, paints, adhesives, gravure inks, and spectacle lenses. Isocyanate compounds are industrially produced by reacting amine compounds with phosgene. The phosgene method has problems in handling highly toxic phosgene, treating hydrochloric acid produced as a large amount of by-products, and corroding equipment. The isocyanate compound produced by the phosgene method usually contains several hundred ppm of hydrolyzable chlorine, which adversely affects the weather resistance, heat resistance, yellowing resistance and the like of polyurethane and polyurea products.

In recent years, it has been desired to develop an industrial production method of an isocyanate compound instead of the phosgene method. As a method for producing an isocyanate compound starting from a formamide compound, a one-step method of directly obtaining an isocyanate compound, a urethane compound is produced in a first reaction step, and then a urethane compound is thermally decomposed in a second reaction step to thermally decompose the isocyanate compound. Have been proposed.

As a one-step method, there is a method of obtaining an isocyanate compound by a dehydrogenation reaction of a formamide compound. U.S. Pat. No. 3,960,914 discloses a method for dehydrogenating a formamide compound in a water-insoluble solvent in the presence of a platinum group catalyst such as Pd, but the reaction rate is low and the selectivity of the isocyanate compound is 30%. There are low disadvantages. JP 54
No. 39018 is a method in which a formamide compound is vapor-phase dehydrogenated for a specific contact time in the presence of an Ag-based catalyst, but the yield of an isocyanate compound is as low as 21%, which is not practical.
U.S. Pat. No. 3,277,140 discloses a method in which a formamide compound is reacted with a halogen such as bromine in the presence of a heterocyclic nitrogen compound. However, the yield of the isocyanate compound is not sufficient, and It is not economically preferable because 4 times mole of the heterocyclic nitrogen compound is consumed as a halide.

A method for producing a urethane compound from a formamide compound in the first reaction step of a two-stage process is disclosed in US Pat.
No. 4,661,217 discloses a method for producing a corresponding urethane compound by oxidizing a formamide compound on a graphite electrode using NaBr as a supporting electrolyte in an alcohol solvent. According to this method, a urethane compound can be obtained at a relatively high yield, but it is difficult to perform it on an industrial scale because the electrode is significantly deteriorated.

On the other hand, although the starting materials are different from the present invention, a method of producing a urethane compound by reacting an amine compound with dimethyl carbonate is also known (JP-B-51-33095,
JP-A-57-82361, U.S. Pat. No. 4,395,565). This method is a method in which an amine compound is reacted with dimethyl carbonate in the presence of a Lewis acid catalyst, a lead, titanium or zirconium-based catalyst, an alkali metal or alkaline earth metal alcoholate catalyst, or the like. According to the examples, generally, the reaction rate is low, and the N-methyl form is easily generated by a side reaction, so that the space-time yield of the urethane compound is low.

Japanese Patent Application Laid-Open No. 1-85956 discloses a method for producing an aliphatic or alicyclic urethane compound in which an N-methylation reaction hardly occurs. In this patent, the amine compound 1
The amine compound and the alkali metal alcoholate or alkaline earth metal alcoholate catalyst are added continuously or intermittently using dimethyl carbonate at least 4 times the moles. However, in order to obtain a urethane compound at a high yield, a large amount of an alcoholate catalyst must be used for an amine compound, so that there is a drawback that the catalyst cost increases. In addition, the alcoholate catalyst inhibits the thermal decomposition reaction of the urethane compound in the second reaction step, so that it is neutralized,
It is necessary to completely remove the neutralizing salts. Therefore, when the use amount of the alcoholate catalyst is large, a large load is imposed on the recovery and purification steps of the urethane compound. Furthermore, since excess dimethyl carbonate is used, it is economically necessary to recover and reuse the unreacted dimethyl carbonate in the reaction product solution, but dimethyl carbonate and methanol form an azeotropic composition, Since the difference in boiling point from methanol is as small as 2 ° C. or less, a complicated distillation process is required for separating and recovering unreacted dimethyl carbonate, and there is also a drawback that fixed costs increase.

[0008] As a method for thermally decomposing the urethane compound in the second reaction step, there are a gas phase method and a liquid phase method, and it is known that the liquid phase method is industrially advantageous. The thermal decomposition reaction of the urethane compound is a reversible reaction, and the equilibrium thereof is more advantageous for the generation of the isocyanate compound at a higher temperature. For this reason, the reaction conditions are severe and various irreversible side reactions occur simultaneously, and, for example, ureas, carbodiimides, uretdiones, isocyanurates and the like are easily formed. These side reactions not only reduce the yield of the isocyanate compound, but also cause clogging of the reactor due to precipitation of solids, making it difficult to stably operate for a long time. Therefore, various methods of using a catalyst, a stabilizer, and the like have been proposed as a method of accelerating a thermal decomposition reaction of a urethane compound and suppressing a side reaction to obtain an isocyanate compound in a high yield.

That is, as a method of using a catalyst for the thermal decomposition reaction of a urethane compound, for example, Japanese Patent Publication No. 57-45736 discloses a periodic table of elements IB, IIB, IIIA, IVA, IVB,
A member selected from the group consisting of metal atoms of groups VB and VIII
Disclosed are catalysts in which one or more metals or compounds thereof are dissolved in a solvent. JP-A-54-88201 describes a method using an alkaline earth metal and its metal compound as a catalyst. JP-A-57-158747 discloses a copper element, a zinc element, an aluminum element, a carbon element other than carbon, an elemental element selected from oxides or sulfides of these elements, A method is disclosed in which one or more compounds are used as a heterogeneous catalyst in a solvent. JP-A-7-258194 describes a method using an organic sulfonic acid and a salt thereof as a catalyst. As a method using a stabilizer, for example, JP-A-57-123159 proposes an alkylating agent such as carboxylic acid chloride and sulfonic acid ester. JP
1-125359 describes a method using phosphite triester as a stabilizer.

[0010]

As described above, it is difficult to industrialize a method for producing an isocyanate compound starting from a formamide compound, and there are also many problems in a method for producing a urethane compound by reacting an amine compound with dimethyl carbonate. have. The present inventor has previously proposed a novel production method for obtaining a urethane compound by reacting a formamide compound with dimethyl carbonate in the absence or presence of a catalyst (JP-A-3-200756 and JP-A-4-235954). ). This method does not require a catalyst particularly in a high-temperature reaction, and is economical because it requires only a small amount of an alcoholate catalyst even in a low-temperature reaction, and has a feature that the urethane compound can be easily recovered and purified from a reaction product solution. Further, since unreacted dimethyl carbonate and generated methyl formate do not form an azeotropic composition, unreacted dimethyl carbonate can be easily recovered and reused.
However, for industrialization, it is necessary to further improve the space-time yield of the urethane compound, and when methyl formate produced as a by-product is decomposed to produce methanol, an azeotrope with dimethyl carbonate is produced and separation becomes difficult. Therefore, it is desired to suppress the decomposition of methyl formate.

Usually, the thermal decomposition reaction of the urethane compound is carried out using a packed tower or an Oldershaw type reactor. The raw material urethane compound is supplied to the solvent in the reaction tank or to the middle stage of the column to be thermally decomposed. After the generated isocyanate compound and methanol are separated from the solvent in the tower, 1
The isocyanate compound is recovered in the second condenser, and then the methanol is recovered in the second condenser. On the other hand, the solvent is continuously or intermittently withdrawn from the reaction tank, and the high-boiling substances generated by the side reaction are separated by a thin-film evaporator or the like, and then the active components such as the solvent are recycled to the reaction tank.

The inventors applied a conventional technique to the thermal decomposition reaction of the urethane compound, and conducted a long-term flow reaction using a glass- and stainless-steel packed-tower type reactor. It was found that the state of the reaction varied greatly depending on the material. That is, when a glass reactor was used, polymer was hardly attached to the packed tower and the reaction tank, and the isocyanate compound was obtained in high yield. However, since the reaction temperature is high, it is difficult to use a glass reactor as an industrial device for thermal decomposition of urethane. On the other hand, when a stainless steel reactor was used, not only the yield of the isocyanate compound was low, but also a large amount of the polymer adhered to the packed tower and the reaction tank, and it was difficult to stably operate for a long time. Particularly, in the case of an unstable isocyanate compound such as meta-xylylene diisocyanate, Harz adhered to the packed tower and was blocked. Preferred materials for industrial equipment include carbon steel, stainless steel, Hastelloy, and the like.However, when a thermal decomposition reaction of a urethane compound is performed in a reactor of these materials, a large amount of by-products of the polymer is generated, and Adhesion of the polymer inside the equipment is inevitable. Therefore, it is difficult to stably produce an isocyanate compound at a high yield for a long period of time.

An object of the present invention is to provide a method for synthesizing a urethane compound from a formamide compound and dimethyl carbonate as starting materials and then thermally decomposing the urethane compound to produce the corresponding isocyanate compound. It is an object of the present invention to provide a method capable of producing an isocyanate stably at a high yield in an industrially advantageous manner for a long period of time.

[0014]

DISCLOSURE OF THE INVENTION The present inventors have made intensive studies to develop a method for industrially and advantageously producing an isocyanate compound from a formamide compound and dimethyl carbonate. As a result, the reaction between the formamide compound and dimethyl carbonate was found. Is carried out in the presence of methanol in a reactive distillation manner to improve the space-time yield of the urethane compound, to significantly suppress the decomposition of the generated methyl formate, and to further reduce the aromatic sulfone in the thermal decomposition reaction of the urethane compound. By using an amide compound, it was found that by-products of a polymer were avoided even in a metal reactor, and it became possible to stably produce an isocyanate with high yield in an industrial apparatus for a long period of time. Reached.

That is, the present invention provides a method of reacting a formamide compound with dimethyl carbonate, and thermally decomposing the obtained urethane compound to obtain an isocyanate compound, wherein the first reaction step of reacting the formamide compound with dimethyl carbonate is carried out in the presence of methanol. The method for producing an isocyanate compound, characterized in that the generated methyl formate is extracted out of the system by reactive distillation, and a second reaction step of thermally decomposing the urethane compound to obtain an isocyanate compound, with an inert solvent, general _{formula: Xn -Ar -SO 2 -NH 2 (} Ar is benzene, aromatic nucleus, X such as naphthalene lower alkyl group or an amino group,, n is an integer of 0 to 3, n is 2
In the above case, X may be the same or different).

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing an isocyanate compound of the present invention is represented by the following chemical formula. (I) of the first reaction step
In the formula, the corresponding urethane compound and methyl formate are formed from the formamide compound and dimethyl carbonate. In the formula (II) of the second reaction step, the corresponding isocyanate compound and methanol are generated by thermal decomposition of the urethane compound.

Embedded image R (NHCOH) _n + n (CH ₃ O) ₂ CO = R (NHCOOCH ₃ ) _n + nHCOOCH ₃ (I) R (NHCOOCH ₃ ) _n = R (NCO) _n + nCH ₃ OH (II)

The formamide compound which is a main raw material of the present invention is an aromatic formamide compound and an aliphatic formamide compound. In the present invention, an aliphatic formamide compound having two formamide groups is particularly preferably used in the present invention. Aliphatic formamide compounds, when classified by molecular structure, include chain aliphatic formamide compounds, alicyclic formamide compounds, and formamide compounds in which a formamide group is bonded to a saturated carbon and has an aromatic ring in the skeleton. Raw materials corresponding to industrially useful isocyanate compounds include, for example, 1,6-hexamethylenebisformamide, N, N ′-[1,3-cyclohexylbis (methylene)] bisformamide, and 1,4-hexamethylenebisformamide having the same structure Isomers, 3-formamidomethyl-3,5,5-trimethyl-1-formamidocyclohexane, N, N '-[1,3-phenylenebis (methylene)] bisformamide and 1,4-isomers of the same structure, etc. Is mentioned. Although aliphatic diisocyanate compounds having high added value can be obtained from these aliphatic diformamide compounds, general-purpose aromatic diisocyanate compounds can also be produced by the method of the present invention.

As the dimethyl carbonate as an auxiliary material, a commercially available product may be used as it is, or may be purified if necessary. The amount of dimethyl carbonate used in the present invention is in the range of 1 to 20 mol, preferably 1 to 10 mol, per 1 mol of the formamide group of the formamide compound. If the amount used is less than 1 mol, the unreacted formamide compound remains, and if it is more than 20 mol, the space-time yield decreases, which is not practical.

The reaction temperature in the first reaction step of reacting the formamide compound with dimethyl carbonate is in the range of 30 to 200 ° C., preferably 50 to 170 ° C. When the formamide compound is reacted with dimethyl carbonate at a reaction temperature of 120 ° C. or higher, no particular catalyst is required. At a reaction temperature lower than this, the reaction rate becomes low, so that it is preferable to use an alkali metal alcoholate or an alkaline earth metal alcoholate as a catalyst in the first reaction step. Specific examples of these include methylates and ethylates of sodium, potassium, lithium, calcium, barium and the like. Practically, sodium methylate is preferred in terms of availability and low cost. The catalyst can be used in the form of a solid or a solution, but a commercially available solution of sodium methylate in methanol is most preferred. When using a sodium methylate catalyst, as the solution concentration of the reaction solution,
It is in the range of 0.01 to 5% by weight, preferably 0.05 to 1%.

The corresponding urethane compound can be produced by reacting the formamide compound with dimethyl carbonate in the absence of a solvent. According to the present invention, the decomposition of methyl formate produced by the coexistence of methanol in this reaction is greatly suppressed. Is done. The amount of methanol coexisted in the first reaction step according to the present invention is in the range of 0.1 to 20 mole ratio, preferably 1 to 10 mole ratio, per mole of formamide compound. When it is less than this range, the effect of suppressing the decomposition of methyl formate is small, and when it is more than this range, the space-time yield of the urethane compound is small. When the formamide compound as the main raw material is solid, or when the urethane compound formed after the reaction precipitates as a solid, a solvent can be used. The solvent that can be used here needs to be inert to the raw material, the catalyst and the urethane compound to be produced. Specific examples thereof include alcohols other than methanol, such as ethanol and propanol, tetrahydrofuran, dioxane and the like. Ethers and hydrocarbons such as benzene and toluene. The use amount of these solvents is preferably the minimum necessary amount, and is usually in the range of 0.1 to 10 times the weight of the formamide compound.

The reaction between the formamide compound and dimethyl carbonate in the first reaction step is an equilibrium reaction. The space-time yield of the urethane compound is obtained by extracting the methyl formate produced in the present invention in the presence of methanol to the outside of the system. And the decomposition of the generated methyl formate is greatly suppressed. In a batch reaction operation, for example, a formamide compound, methanol and, if necessary, a catalyst or a solvent are charged into a reactor, heated to a predetermined reaction temperature, dimethyl carbonate is added thereto, and methyl formate generated with the progress of the reaction is added. It is preferably carried out by a reactive distillation type in which steam is extracted out of the system and is reduced. In addition, an inert gas such as nitrogen gas can be used as a carrier for positively extracting methyl formate in the reaction system. On the other hand, in a continuous reaction operation, for example, a formamide compound, dimethyl carbonate, methanol, and, if necessary, a catalyst or a solvent are supplied to the reactor through a line mixer or the like, and the reaction is performed for a predetermined residence time. At the same time as extracting the liquid, a method is implemented in which the generated methyl formate vapor is extracted out of the system and shrunk. In the same manner as in the batch reaction operation, a carrier such as nitrogen can be blown into the reactor, and methyl formate can be positively discharged out of the system.

The urethane compound in the reaction product liquid obtained in the first reaction step is subjected to various combinations of unit operations such as distillation, evaporation, neutralization, washing with water, solvent extraction, crystallization, etc., to obtain a crude urethane compound. It can be recovered and further purified. Specifically, unreacted dimethyl carbonate, methanol and methyl formate are distilled off from the reaction product by flash distillation to recover a crude urethane compound. The crude urethane compound can be used as a raw material in the second reaction step by separating high-boiling by-products using a thin-film evaporator. Alternatively, the crude urethane compound and the bottoms withdrawn from the reaction tank in the second reaction step described later are supplied together to a thin-film evaporator to obtain a crude urethane compound and a high boiling point in the bottoms. By-products can also be removed at the same time.

When an alkali metal or alkaline earth metal alcoholate catalyst is used in the first reaction step, the crude urethane compound is obtained by neutralizing the reaction product solution with an acid and filtering the neutralized salt as it is or after depositing a neutralized salt. Unreacted dimethyl carbonate, methanol and methyl formate are distilled off from the mother liquor by flash distillation and collected. The crude urethane compound is washed with water as it is or once dissolved in a water-insoluble solvent to extract excess acid and neutralized salt into an aqueous layer, and then separated into an organic layer and an aqueous layer. The solvent in the layer is distilled off to recover the urethane compound. At this time, a small amount of the urethane compound dissolves in the aqueous layer, but can be recovered by back extraction using the same solvent. The solvent and water are removed from the organic layer and the back-extracted liquid by flash distillation to recover the urethane compound. Examples of the acid used here include organic acids such as formic acid, acetic acid, and benzoic acid, and mineral acids such as hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid. Further, the water-insoluble solvent is, for example, n
-Hydrocarbon compounds such as hexane, cyclohexane, benzene, toluene and xylene. In the method of separating and recovering the urethane compound from the reaction product solution, each unit operation can be suitably performed by a batch system, a continuous system, or a combination of both.

On the other hand, methyl formate is first separated by distillation from the low boiling components recovered by flash distillation. Next, methanol is easily distilled off from dimethyl carbonate as an azeotropic composition with dimethyl carbonate (boiling point difference: about 28 ° C.).
Methyl formate generated in the first reaction step is partially decomposed into methanol, but in the present invention, unreacted dimethyl carbonate is extracted from an azeotropic composition of methanol and dimethyl carbonate by extracting a methanol component corresponding to the decomposition of methyl formate. Since it can be recycled as it is, no azeotropic separation process is required.

Next, the thermal decomposition reaction of the urethane compound in the second reaction step will be described. In the present invention, the urethane compound obtained in the first reaction step is mixed with an inert solvent and a general formula: Xn-A
r -SO ₂ -NH ₂ (Ar is benzene, aromatic nucleus, X is a lower alkyl group such as naphthalene or an amino group,, n is 0
(Where n is 2 or more, X may be the same or different) when n is 2 or more, whereby an isocyanate compound and methanol are obtained by thermal decomposition.
Specific examples of the compound represented by the above general formula include benzenesulfonamide, toluenesulfonamide, dimethylbenzenesulfonamide, sulfanilamide, naphthalenesulfonamide, and the like, and may be used alone or in combination of two or more. Can be. The amount of these compounds used is in the range of 0.0001 to 10% by weight, preferably 0.001 to 1% by weight, based on the urethane compound. If the amount used is smaller than this range, the effect of suppressing the adhesion of the polymer in the reactor is small, and if it is larger than this range, there is no further effect, which is uneconomical.

The inert solvent used in the second reaction step is
Those having a higher boiling point than the isocyanate compound to be produced are desirable. By using such an inert solvent, the mixed vapor of the produced isocyanate compound and methanol is selectively expelled from the reactor, and the difference between the condensation temperatures thereof is used to make the isocyanate compound in the first stage and the second stage in the second stage. To condense the methanol, and each is recovered. This solvent has a boiling point difference of 40 with respect to the isocyanate compound formed.
Those having a temperature of at least ° C are preferred. When the boiling point difference is smaller than this, a large amount of solvent is entrained in the fraction of the isocyanate compound, and the load of the purification step of the isocyanate compound increases. Specific examples of the solvent used in the second reaction step, dioctyl phthalate, didodecyl phthalate,
Examples include hydrocarbons such as esters such as diphenyl phthalate, dibenzyltoluene, pyrene, triphenylmethane, phenylnaphthalene, benzylnaphthalene, and triphenyl hydride, and aromatic hydrocarbons used as a heat medium are particularly preferable. The amount of these solvents used is 0.1 to 10 times the weight of the urethane compound, preferably
0.5 to 5 times the weight.

By using the compound represented by the above general formula and the inert solvent in the second reaction step, a metal-made reaction apparatus such as a stainless steel apparatus can be used. When the thermal decomposition reaction of the urethane compound is performed using a metal reactor in the second reaction step, a catalyst such as a metal ion is not particularly required, but when an aliphatic isocyanate is produced, the catalyst may be used as a catalyst. Metal ions selected from iron, nickel, cobalt, zinc, tin and the like, and organic sulfonic acid compounds can be suitably used.

The temperature of the reaction for thermally decomposing the urethane compound is in the range of 150 to 350 ° C., preferably 200 to 300 ° C. If the reaction temperature is lower than this range, the reaction rate is low, and if it is higher than this range, side reactions increase, which is not preferable. The reaction pressure is a pressure at which the isocyanate compound generated at the reaction temperature can vaporize,
It is typically between 1 and 500 Torr. The reaction time varies depending on the type of the urethane compound, the reaction temperature, the pressure, the reaction type and the like, but is usually 0.5 to 5 hours.

The reaction operation for thermally decomposing the urethane compound in the second reaction step can be carried out by a batch system using a tank-type or tube-type reactor, but a flow system is industrially advantageous. In the flow type, for example, it is preferable to use an external reflux type or internal reflux type multi-stage distillation column as a reaction apparatus, and to carry out the reaction distillation type. For example, a solvent and a compound represented by the above general formula are charged into a reaction tank of a distillation still equipped with a stirrer, and heated under reduced pressure to maintain a boiling state. The raw material tank has a nitrogen atmosphere. When the urethane compound is solid at room temperature, it is heated to maintain a solution state. At that time, in order to minimize the deterioration of the urethane compound, it is desirable to set the heating temperature to around the melting point of the urethane compound and to shorten the residence time in the raw material tank. The raw material liquid is continuously supplied to the reaction tank using a metering pump. In the case where the generated isocyanate compound has a property that is unstable and easily causes deterioration such as polymerization, the compound represented by the above general formula can be continuously or intermittently applied to the top of the multi-stage column as it is or dissolved in an isocyanate compound or a solvent. Is preferably supplied to When a metal ion is used in combination as a catalyst, the metal compound is dissolved in an isocyanate compound, a solvent or the like and supplied to the reaction tank.

The vapor generated in the reaction tank includes, for example, in the case of a urethane compound having a bifunctional group, methanol, a diisocyanate compound, an intermediate monoisocyanate compound, and a solvent. By passing through the column, it is concentrated to a vapor rich in methanol and a diisocyanate compound. This vapor is first introduced into a condenser maintained at a temperature higher than the boiling point of methanol to recover the diisocyanate compound. Next, it is introduced into a condenser maintained at a temperature lower than the boiling point of methanol to recover methanol. The diisocyanate compound recovered in the first-stage condenser can be further purified by distillation, if necessary, to obtain a high-purity diisocyanate compound.

On the other hand, high-boiling substances are produced by side reactions in the reaction tank. If this accumulates, an addition reaction occurs with the isocyanate group, so that not only the yield decreases, but also the polymer precipitates or adheres to the reaction tank. Long-term driving becomes difficult. For this reason, it is necessary to continuously or intermittently extract the solvent in the reaction tank and remove high-boiling substances. As this method,
For example, the bottoms are flash-evaporated and high-boiling by-products are separated as the bottom of the evaporator, while the vapor containing the diisocyanate compound, monoisocyanate compound, unreacted urethane compound and solvent is condensed and recycled to the reaction tank. I do.

[0032]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by these examples.

(First Reaction Step: Synthesis and Purification Experiment of Urethane Compound) Example 1 As a reactor, an electromagnetic stirrer, a thermocouple protection tube, a pressure gauge,
A 1 liter autoclave made of stainless steel (SUS-304) equipped with a nitrogen gas injection nozzle and a reflux condenser was used. A nitrogen cylinder, a pressure regulator, and a nitrogen blowing nozzle were connected by piping. A reflux condenser outlet, a flow control valve, a cold trap cooled with methanol / dry ice, a gas meter, and a vent for purging waste gas were connected by piping. N, N '-[1,3-cyclohexylbis (methylene)] bisformamide (hereinafter 1,3-B
198 g, dimethyl carbonate 360 g and methanol 64 g were charged and sealed. At this time, 1,3-BFC
The amount of methanol added per mole is 2 mole ratio.
The reactor was placed in an electric furnace, the inside of the reactor was replaced with nitrogen gas, and then pressurized to 10 kg / cm ² G through a pressure regulator.
At the same time as stirring and heating of the electric furnace were started, waste gas was purged at a flow rate of 0.5 L / min using a flow control valve, and the generated methyl formate was discharged out of the system. After the temperature in the reactor reached 155 ° C., the state was maintained for 4 hours.

After the reaction, the reaction mixture was cooled, and the reaction product liquid and the liquid accumulated in the trap were analyzed by an internal standard method of liquid chromatography and gas chromatography.
The yield of methyl N, N '-[1,3-cyclohexylbis (methylene)] biscarbamate (hereinafter abbreviated as 1,3-BUC) is 99.4%, and the other is an intermediate methyl monocarbamate. there were. In the reaction product solution and trap,
It contained 94.8% of the theoretically formed methyl formate.
Using a rotary evaporator, the reaction product is heated at normal pressure and then under reduced pressure to distill off methyl formate, methanol and unreacted dimethyl carbonate to obtain a crude product in a molten state.
1,3-BUC was recovered. Next, the crude urethane compound was dissolved in a toluene solvent to adjust the concentration to 30% wt.
The mixture was washed with water at 0 ° C. for 3 times, and separated into an organic layer and an aqueous layer. Using a rotary evaporator, the organic layer was heated at normal pressure and then under reduced pressure to remove toluene and obtain purified 1,3-BUC as white crystals.

Example 2 In the same manner as in Example 1, N, N '-[1,3-phenylenebis (methylene)] bisformamide (hereinafter M
192 g, 360 g of dimethyl carbonate and 96 g of methanol were charged and reacted under the conditions of a reaction pressure of 10 kg / cm ² G, a reaction temperature of 155 ° C., a flow rate of waste gas of 0.5 L / min, and a reaction time of 4 hours. At this time, the amount of methanol added is 3 moles per mole of MXDF. After the reaction,
The reaction product liquid and the liquid in the trap were analyzed by an internal standard method of liquid chromatography and gas chromatography. As a result, methyl N, N '-[1,3-phenylenebis (methylene)] biscarbamate (hereinafter referred to as MXDF standard)
The yield was 98.9%, and the other was an intermediate methyl monocarbamate compound.

Example 3 In the same manner as in Example 1, 172 g of 1,6-hexamethylenebisformamide (hereinafter abbreviated as HMDF) was added to the reactor.
, 450 g of dimethyl carbonate and 64 g of methanol, and reacted under the conditions of a reaction pressure of 10 kg / cm ² G, a reaction temperature of 155 ° C., a flow rate of waste gas of 0.5 liter / min, and a reaction time of 3 hours. At this time, the amount of methanol added was 2 mol per 1 mol of HMDF. As a result, HMDF standard 1,6-
Methyl hexamethylenebiscarbamate (hereinafter HMD
The yield was 98.8%, and the other was an intermediate methyl monocarbamate compound.

Example 4 Two 500 ml stirred-tank type reactors made of glass and packed in a packed tower (packed with Dickson packing and having eight stages) were connected in series to carry out a two-tank continuous reaction under normal pressure. Was. The condenser of each packed tower, a cold trap cooled by methanol / dry ice, a gas meter, and a vent for waste gas were connected by piping. Using three metering pumps, a molten formamide compound, a methanol solution of dimethyl carbonate and a methanol solution of 28% sodium methylate were separately supplied to the first reactor. The reaction product liquid in the first tank was supplied to the reactor in the second tank using a pump while maintaining a predetermined amount of retained liquid. The reaction product liquid in the second tank kept a predetermined amount of the retained liquid, and was continuously discharged to a receiver using an electromagnetic control valve.
The condenser at the top of the packed tower in the first tank was maintained at a temperature of 35 ° C. and brought into a completely reflux state. On the other hand, the condenser in the second tank was kept at a temperature of 35 ° C. and a fraction was withdrawn at a reflux ratio of 2. 1,3-BFC 99g / hr,
Dimethyl carbonate 180 g / hr, methanol 64 g / hr and 28%
Sodium methylate methanol solution 2 g / hr feed rate, residence time in each reactor 2 hr, first tank reaction temperature 75 ° C
A flow reaction was performed under the condition of a reaction temperature of 80 ° C. in the second tank. At this time, the molar ratio of dimethyl carbonate is 4 times, the molar ratio of methanol is 4 times, and the molar ratio of sodium methylate is 0.02 mole per mole of 1,3-BFC.

After reaching the steady state, the reaction product solution and the solution collected in each trap were sampled and analyzed by the internal standard method of liquid chromatography and gas chromatography. As a result, the 1,3-BUC yield based on 1,3-BFC was 99.
2%, and the others were methyl monocarbamate compounds as intermediates. The reaction product solution and the trap contained 95.6% of the theoretically generated methyl formate. The reaction product was neutralized by adding a 50% aqueous sulfuric acid solution, and then heated at normal pressure and then under reduced pressure using a rotary evaporator to evaporate methyl formate, methanol, and unreacted dimethyl carbonate, thereby forming a molten state. Of crude 1,3-BUC was recovered. Next, dissolve the crude urethane compound in toluene
After adjusting the concentration, the solution was maintained at a temperature of 70 ° C., washed three times with water, and separated into an organic layer and an aqueous layer. The organic layer was heated at normal pressure and then under reduced pressure using a rotary evaporator to remove toluene and obtain purified 1,3-BUC as white crystals.

Comparative Example 1 The procedure of Example 1 was repeated except that no methanol was added. That is, 198 g of 1,3-BFC and 360 g of dimethyl carbonate were charged into a reactor, and the reaction pressure was 10 kg / cm ² G,
The reaction was performed under the conditions of a reaction temperature of 155 ° C., a flow rate of waste gas of 0.5 liter / min, and a reaction time of 4 hours. As a result, 1,3-BFC
The standard 1,3-BUC yield was 98.2%, and the other was an intermediate methyl monocarbamate compound. 77.2% of theoretically generated methyl formate in the reaction solution and trap
Of methyl formate.

COMPARATIVE EXAMPLE ² After charging the gas of Example 1 with 10 kg / cm ² G of nitrogen gas,
The operation was carried out without closing the formed methyl formate to the outside of the system. That is, 192 g of 1,3-BFC, 360 g of dimethyl carbonate and 64 g of methanol were charged, the reaction temperature was 155 ° C., and the reaction time was
The reaction was performed for 4 hours. As a result, the 1,3-BFC standard
The 1,3-BUC yield was 89.2%, and the other was an intermediate methyl monocarbamate compound.

(Second Reaction Step: Thermal Decomposition Experiment of Urethane Compound) Example 5 As a reactor, a packed tower (packed with Dickson packing,
Thermal decomposition experiment of urethane compound by flow reaction using 500ml electromagnetic stirring type autoclave equipped with raw material supply nozzle, reaction product liquid discharge nozzle, thermocouple protection tube and jacket for circulation of heat medium. Was done. All reactors were made of stainless steel (SUS-304). A condenser, a trap cooled with methanol / dry ice, a vacuum pump, and a vent for waste gas were connected to the top of the packed tower by piping. An electromagnetic control valve, a receiver, a trap, a vacuum pump, and a vent for waste gas were connected to the bottom discharge nozzle by piping. The condenser at the top of the packed tower circulated hot water at a temperature of 60 ° C., and was set so that the reaction product was discharged to the receiver under the condition of a reflux ratio of 1. After the experiment, a stainless steel (SUS-304) wire net was weighed to check the adhesion state of the polymer in the reaction tank. To check the amount of polymer adhered in the packed tower, the packed material was weighed in advance and then packed into the tower.

In a constant temperature (140 ° C.) raw material tank purged with nitrogen gas, 1,3-BUC, a urethane compound, and barrel thermometer were placed.
After charging 400 (main component: dibenzyltoluene) in a weight ratio of 1: 2, p-toluenesulfonamide (hereinafter abbreviated as p-TSA) so as to be 400 ppm based on 1,3-BUC. Was added to prepare a raw material liquid. A small amount of nitrogen gas was flowed into the raw material tank. The reaction tank was charged with 300 g of Barreltherm 400 containing 200 ppm of p-TSA. The raw material liquid was continuously supplied to the reactor at a flow rate of 128 g / hr using a metering pump while stirring the reaction tank and maintaining the content liquid temperature at 250 ° C. and the pressure in the system at 20 mmHg. The isocyanate compound and methanol produced by the reaction were collected by a receiver and a cold trap, respectively. 10 mmH pressure in the can withdrawal line
g, and the bottom liquid was continuously discharged to the receiver using an electromagnetic control valve so that the amount of liquid retained in the reaction tank was maintained at 340 ml.

After the start of the reaction, the liquid volume in each of the receivers and the cold trap was measured at predetermined intervals, and the composition was analyzed by an internal standard method using a liquid chromatograph and a gas chromatograph. As a result of analyzing the data in the steady state, the N, N '-[1,3-
Cyclohexylbis (methylene)] bisisocyanate (hereinafter, abbreviated as 1,3-BIC) selectivity was 90.5%, and the selectivity of the intermediate monoisocyanate compound was 2.1%. This flow reaction experiment was continued for 10 hours, and the supply of raw materials was stopped. After confirming that the distillation of the isocyanate compound was completed, the entire amount of the liquid in the tank was extracted at a high temperature.
The reactor was washed with acetone under total reflux, then dried and opened, and the weight of the wire mesh and filler in the tank was measured. As a result, the amount of polymer adhering to 55.2 g of the filler was 0.0
The amount of polymer adhered to 1 g or less and 27.4 g of a wire net was 0.01 g or less.

Comparative Example 3 The procedure of Example 5 was repeated, except that p-TSA was not used. As a result, the 1,3-BUC reaction rate was 99.
At 4%, the selectivity for 1,3-BIC was 83.4%, and the selectivity for the intermediate monoisocyanate compound was 4.4%. Filling 54.
The amount of polymer adhered to 3 g was 0.12 g, and the amount of polymer adhered to 28.5 g of wire mesh was 0.55 g.

Example 6 In a raw material tank, 1,3-BUC and barrel therm 400 were mixed at a ratio of 1: 2.
Then, 50 ppm of p-toluenesulfonic acid and 200 ppm of p-TSA were added to 1,3-BUC to prepare a raw material liquid. The procedure was performed in the same manner as in Example 5 except that 25 ppm of p-toluenesulfonic acid and 100 ppm of p-TSA were charged into the reaction vessel. As a result, 1,3-B
At an IC conversion rate of 99.8%, 1,3-BIC selectivity was 95.0%,
The monoisocyanate compound selectivity was 1.5%. The amount of polymer adhering to 54.3 g of filler is 0.01 g or less, 28.4 g of wire mesh
The amount of the polymer adhered to the polymer was 0.01 g or less.

Example 7 After charging 1,3-BUC and Barreltherm 400 at a weight ratio of 1: 1 in a raw material tank, 50 ppm of dibutyltin dilaurate and 400 ppm of p-TSA were added to 1,3-BUC. Add,
A raw material liquid was prepared. Dibutyltin dilaurate in the reactor
Barrel Therm containing 50ppm and 400ppm p-TSA
The same procedure as in Example 5 was carried out except that 300 g of 400 was charged and the flow rate of the raw material liquid was 160 g / hr. As a result,
At a BUC conversion of 99.6%, 1,3-BIC selectivity was 93.8.
% And the monoisocyanate compound selectivity was 1.8%.
The amount of polymer adhering to 53.6 g of filler is 0.01 g or less, wire mesh 28.
The amount of polymer adhered to 1 g was 0.01 g or less.

Example 8 p-TSA was added to the top of the packed column of the reactor used in Example 5.
Was supplied as a solution of N, N '-[1,3-phenylenebis (methylene)] diisocyanate (hereinafter abbreviated as MXDI), a p-TSA tank, a metering pump and piping were installed. In the raw material tank, after mixing MXDU and Barreltherm 400 at a weight ratio of 1: 3, p-
A raw material liquid was prepared by adding 600 ppm of TSA. p-TS
In the tank A, an MXDI solution containing 0.5 wt% of p-TSA was prepared. The reactor was charged with 300 g of Barrel Therm 400 containing 200 ppm of p-TSA. The raw material liquid was supplied to the reaction tank at a flow rate of 100 g / hr, and at the same time, the MXDI solution of p-TSA was supplied to the top of the packed tower at a flow rate of 3 g / hr. The other conditions were the same as in Example 5. As a result, at an MXDU conversion of 99.2%, the MXDI yield was 88.1%, and the selectivity for the intermediate monoisocyanate compound was 2.1%. The amount of polymer adhered to 55.1 g of the filler was 0.01 g or less, and the amount of polymer adhered to 28.2 g of wire mesh was 0.01 g or less.

Example 9 After mixing MXDU and Barreltherm 400 in a weight ratio of 1: 3 in a raw material tank, 75 ppm of dibutyltin dilaurate and 600 ppm of p-TSA were added to MXDU to prepare a raw material liquid. . 0.5 wt% of p-TSA is contained in the p-TSA tank.
An MXDI solution containing was prepared. The reaction tank was charged with 300 g of barrel thermo 400 containing 25 ppm of dibutyltin dilaurate and 200 ppm of p-TSA. Material flow rate 120
g / hr and p-TSA MXD
Solution I was fed to the packed tower top at a flow rate of 3.6 g / hr. Otherwise, the procedure was the same as in Example 5. As a result, MXD
At a U conversion of 99.1%, the MXDI selectivity was 91.5% and the monoisocyanate compound selectivity was 1.4%. Filling
The amount of polymer adhered to 49.3 g was 0.01 g or less, and the amount of polymer adhered to 29.1 g of wire mesh was 0.02 g.

Example 10 Example 10 was carried out in the same manner as in Example 5, except that HMDU was used as the urethane compound instead of 1,3-BUC and the reaction pressure was 30 mmHg. As a result, the HMDU reaction rate
At 99.5%, 1,6-hexamethylene diisocyanate selectivity is 92.1%, monoisocyanate compound selectivity is 2.2%
It became. The amount of polymer adhered to 54.2 g of the filler was 0.01 g or less, and the amount of polymer adhered to 27.8 g of wire mesh was 0.01 g or less.

Comparative Example 4 In Example 9, p-TSA was added to the reactor and the top of the packed column.
Was performed in the same manner except that no was added. as a result,
The MXDI selectivity was 63.8 at 99.0% MXDU conversion.
% And a selectivity for the monoisocyanate compound of 3.1%. The amount of polymer adhering to 56.4 g of the packing was 33.0 g, and the inside of the packed tower was almost closed. The amount of the polymer adhered to 28.3 g of the wire net was 2.2 g.

(Purification Step of Crude Isocyanate Compound:
Example 11 Distillation Experiment Example 11 Using a 2 liter glass packed tower (SUS-316 through-the-pack packing, number of stages: 14), the crude 1,3-BIC obtained by a thermal decomposition experiment of a urethane compound was used. A batch distillation experiment was performed. The raw material 1,3-BIC contained a monoisocyanate compound and a trace amount of by-products in addition to 96.9% of 1,3-BIC. Operating pressure of distillation still 1 Torr, temperature 144-174
As a result, the 1,3 BIC with 99.9% purity by gas chromatographic analysis was used as the main fraction.
Was obtained with a recovery rate of 93.2%. 1,3-BIC distillation balance is 9
It was 9.3%. NCO content of this purified 1,3-BIC 43.
1% (theoretical value: 43.3%), hue APHA was 5 or less, and hydrolyzable chlorine was 1 ppm or less.

[0052]

According to the method of the present invention, a high-quality isocyanate compound containing no hydrolyzable chlorine can be produced economically and stably in high yield from a formamide compound and dimethyl carbonate as raw materials. That is, in the method of the present invention, in the first step of urethane synthesis, the space-time yield of the urethane compound is significantly improved by extracting methyl formate formed in the presence of methanol out of the system by a reactive distillation method, The decomposition rate of methyl is suppressed. In addition, in the urethane pyrolysis of the second step, by adding p-toluenesulfonamide or the like as a stabilizer, side reactions are small even when a reaction device made of a metal material is used, and adhesion of a polymer is suppressed. An isocyanate compound can be produced stably for a long time in a high yield. Therefore, according to the method of the present invention, a high quality isocyanate compound containing no hydrolyzable chlorine can be produced extremely industrially advantageously.
The industrial significance of the present invention is great.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yutaka Kanbara 182 Niigata, Tayuhama, Niigata-shi, Niigata Pref.

Claims (13)

[Claims] In a method of reacting a formamide compound with dimethyl carbonate and thermally decomposing the obtained urethane compound to obtain an isocyanate compound, a first reaction step of reacting the formamide compound with dimethyl carbonate is performed in the presence of methanol, A method for producing an isocyanate compound, wherein the produced methyl formate is extracted out of the system by reactive distillation. 2. The process for producing an isocyanate compound according to claim 1, wherein, in the first reaction step, methanol is coexisted in a range of 0.1 to 20 mole ratio with respect to 1 mole of the formamide compound. 3. The process for producing an isocyanate compound according to claim 1, wherein the urethane compound is recovered by removing the low-boiling compounds such as unreacted dimethyl carbonate by flash evaporation of the reaction product liquid in the first reaction step. 4. The reaction product of the first reaction step is neutralized with an acid,
5. The method for producing an isocyanate compound according to claim 4, wherein the urethane compound is recovered by removing the low-boiling compounds such as unreacted dimethyl carbonate by flash evaporation as it is or after separating the precipitated salt by filtration. 5. The method for producing an isocyanate compound according to claim 3, wherein the recovered urethane compound is purified by distillation or washing with water. 6. A second reaction step of a urethane compound obtaining by thermal decomposition isocyanate compound, and an inert solvent, the general _{formula: Xn -Ar -SO 2 -NH 2 (} Ar is benzene, aromatic nucleus of naphthalene, X is a lower alkyl group or an amino group, n is an integer of 0 to 3, and when n is 2 or more, Xs may be the same or different). A method for producing the isocyanate compound according to the above. 7. The method for producing an isocyanate compound according to claim 6, wherein a reaction device made of a metal material is used in the second reaction step. 8. The method for producing an isocyanate compound according to claim 6, wherein the inert solvent in the second reaction step has a higher boiling point than the isocyanate compound to be produced. 9. The general formula used in the second reaction step: Xn-A
The process according to claim 6 isocyanate compound according r -SO ₂ -NH ₂ becomes compound is p- toluenesulfonamide. 10. The method for producing an isocyanate compound according to claim 6, wherein the crude isocyanate compound obtained in the second reaction step is purified by distillation. 11. The method according to claim 6, wherein the bottoms discharged from the reaction tank in the second reaction step is flash-evaporated as it is or together with the urethane compound from the first reaction step, and the flash fraction is recycled to the reaction tank. Production method of isocyanate compound. 12. The method for producing an isocyanate compound according to claim 1, wherein the formamide compound is an aliphatic or alicyclic formamide. 13. The method according to claim 13, wherein the formamide compound is N, N '-[1,3-phenylenebis (methylene)] bisformamide or N, N
The method for producing an isocyanate compound according to claim 12, which is N '-[1,3-cyclohexylbis (methylene)] bisformamide.